Technical Field
The present invention relates to a workpiece processing system and processing method.
Background Art
Various methods for processing workpieces are available, and when a workpiece is to be carburized, for example, the workpiece moves through a plurality of processing chambers in order, and in these processing chambers, various types of control is performed to the workpiece, such as moving of the workpiece straight ahead or rotating the workpiece by an actuator, or varying pressure in a processing chamber from vacuum atmosphere to high-pressure atmosphere.
Each workpiece is conveyed through a plurality of processing chambers in accordance with the predetermined conveying order for workpieces, and a workpiece subjected to the processing in a processing chamber is conveyed to the next processing chamber by a conveyor for the processing in the next processing chamber. In this way, the workpiece undergoes processing in the plurality of processing chambers, whereby it is processed as a semifinished product or a finished product.
Conventionally when a workpiece is processed while being conveyed through such a plurality of processing chambers in order, if the processing duration of the workpiece in each processing chamber changes from desired duration, the workpiece is processed while shifting the timing to convey the workpiece to the next processing chamber by such a changed processing duration.
Therefore if the processing of the workpiece in each processing chamber takes time more than the desired duration, the cumulative duration that is the summation of the exceeded durations will be standby time at the following processing chambers. Conversely if the processing duration of the workpiece in a processing chamber is shorter than the desired processing duration, the process start time at the following processing chambers will be advanced.
In this way, the processing duration is managed for each processing chamber, and so a change in the processing duration of a processing chamber causes a change in the process start time in other processing chambers, which may cause problems, such as a variation in stand-by time at the other processing chambers or insufficient time for preparation there.
For instance, a variation in stand-by time at the processing chambers means a variation in the amount of heat dissipation from the workpiece after heat treatment at a processing chamber, and so all of a plurality of workpieces to be processed cannot be controlled uniformly about the temperature, resulting in instable quality of the workpieces. Such a problem will be remarkable in the case of a heat treatment at high temperatures, such as rapid carburizing processing where the workpieces are processed under high-temperature atmosphere at about 1,100° C., for example.
Further, if processing duration at each processing chamber is changed, and such a temporal change is cumulated, then the processing at the following processing chambers cannot be performed in some cases. Especially in the case of a high-cycle operation, it is essential for the cyclic operation to follow the processing time in the units of seconds, and so the possibility to stop operation cannot be denied.
Patent Document 1 discloses a method and apparatus for carburizing, quenching and tempering, in which one preheating chamber, six carburizing chambers, a cooling chamber, a reheating chamber, a quenching chamber and a tempering chamber are disposed around an intermediate chamber having a conveyance unit, each of major processing chambers is heated by high-frequency induction heating. Plasma carburizing is performed in the carburizing chambers, and workpieces conveyed from a machining and manufacturing line one by one are distributed to each of the processing chambers for carburizing, quenching and tempering.
According to the method and apparatus disclosed in Patent Document 1, carburizing can be performed in accordance with the supplying speed from the machining and manufacturing line without stopping the flow of the machining and manufacturing line. However, a workpiece preheated at the preheating chamber, for example, will be held at the carburizing temperature in the preheating chamber until the intermediate chamber or the carburizing chamber become vacant, and so if a variation occurs in the processing time at the carburizing step or the following steps, the workpieces are highly likely not to be processed in a scheduled cycle time.